To date no known resonant devices have been driven with direct optical-electro-mechanical coupling. This invention is, and is readable optically. There have been some opto-thermal-mechanical devices driven by temperature changes resulting from absorbed radiation which are described in the literature, however these devices use neither the structures nor principles taught here. For reference to opto-thermal drives, see for example "Optical Micromachined Pressure Sensor for Aerospace Applications", by Diogenes Angelidia and Philip Parsons, Optical Engineering, Vol. 31(1992) pp. 1638-1642. See also "Optical Excitation of Mechanical Microresonators", Kozel, et al, Soviet Tech. Phys. Lett. 17(11), Nov. 1991 0360-120X/91/11 0 804-02 (.COPYRGT. Am. Inst. of Physics, 1992), and "Photothermal Self-Excitation of Mechanical Microresonators", also Kozel, et al, Opt. Spectroscopy (USSR) 69 (3), Sept. 1990, 0030-400x/90/090401-02 (.COPYRGT. 1991, The Optical Society of America).
Other interesting variations for resonant beam drives are described in "Optical Fiber Sensors Using Micromechanical Silica Resonant Elements" by Jones, Naden and Neat, IEE vol. 135(part D)(1988) pp 353-8 and in "Photoacoustic Oscillator Sensors" by Langdon and Dowe, SPIE, Vol. 798, Fiber Optic Sensors II (1987), pp 86-93. It should be noted that in the Jones, Naden and Neat article, these researchers were convinced that it would be possible to construct a self-resonant device that was excited optothermally (using the thermoelastic effect), although they believed silicon for this purpose was unsuitable (page 358). U.S. Pat. No. 5,188,983 assigned to Wisconsin Alumni Research Foundation, inventors being Geckel and Sniegowski, and an International Application No. PCTUS93/08404 assigned to Honeywell Inc., inventors being Zook and Burns, describe relevant teaching within the prior art relative to resonant microbeams incorporating electrostatic drive and piezoresistive sense. In these cases, electrostatic excitation is achieved using force generated by applying small alternating voltages to stimulate the microbeam. Sensing of the microbeam flexure is achieved using strain sensitive resistive elements. Oscillatory behavior requires electronic amplification and phase correction circuitry. The approach disclosed herein uses optical methods to drive the microbeam, sense the microbeam vibrations and, if certain conditions are met, produce self-oscillation with no intervening electro-optical components, thus eliminating the need for piezoresistors, drive electrodes, electrical contacts and any metallurgy for electrical interconnection. The resulting simplification in microbeam construction reduces processing steps, eliminates sources of aging or degradation, allows for better matching between microbeams and allows for significantly thinner microbeams for increased sensitivity while reducing chip size and cost.
For background or construction techniques useful in building structures similar to what is described here, see POLYSILICON RESONANT MICROBEAM TECHNOLOGY FOR HIGH PERFORMANCE SENSOR APPLICATIONS by Guckel, et al, 0-7803-0456-X/92, (.COPYRGT. 1990, IEEE).
In general the device herein has two potential basic forms: a device having a self-resonating member, drivable by either a continuous or pulsed/modulated optical signal; and a device with a flexible member which is driven to resonance by an optical signal of timed pulses. In general, either one affects an optical input at a rhythm related directly to the vibrations the member makes, since the moving member's reflectivity is changing cyclically with each oscillation. (A third form is also described which uses a reverse biased p-n junction photodiode that only resonates in the presence of light. This third form has significant advantages and disadvantages as well.)
These vibrations of the flexible member and their rates are affected by the other environmental influences on the resonating member, for examples; stress and strain, temperature, pressure, acceleration, acoustic influences, and so forth. Variations in the structure of the member may be made to get better signal-to-noise ratio for the influence being measured, so, for example, a short cantilevered beam would be better for temperature sensing and a relatively long beam attached at the two longitudinal ends would be better for sensing strain. Multi-beam devices are also useful. A number of variations are taught herein.
Accordingly, many real sensing needs may be easily met using this invention, including, for example, pressure, weight, temperature and so forth. Further, these devices may be added to larger structures, such as a larger diaphragm, for example, to calibrate it or give more exact readings than would otherwise be available by direct measurement of a larger diaphragm using capacitive, resistive or other sense originated signals.
Many variations in the structure itself are possible while staying within the scope of the teachings of this patent, and are covered by the claims herein.